1. Field of the Invention
This invention relates to a vacuum-tight window arrangement for high power tubes for the purpose of operating in the mm range, with a rectangular waveguide, containing a one-piece dielectric rectangular window which allows waves to pass therethrough, the window having a thickness corresponding approximately to half the wavelength of the wave of the center operating frequency, and a pair of apertures which symmetrically constrict the broad dimension of the waveguide and which are arranged in front of and behind, respectively, the rectangular window in the course of the waveguide.
2. Description of the Prior Art
Presently known microwave windows having an inductivity compensated rectangular dielectric have repeatedly proven themselves; however, in some cases, for example, in the case of certain wideband high power tubes, such windows are not capable of meeting the demands required of them. Therefore, particularly in the case of high operating energies and high operating frequencies, there is the danger of arcing in the area of the aperture. In addition, under such extreme operating conditions, it is possible that disturbing resonances (so-called "trapped modes" or "ghost modes") may be formed, which, by changing the adjustment values, lead to amplification fluctuations in the operating range of the tubes, on the one hand, and, due to consumption of power, heat or destroy the window, on the other hand and thereby altogether permit actual use of only one segment of the theoretically possible bandwidth.
For these reasons, even in the case of high power linearbeam tubes, there has been a prevalent changeover to round window embodiments, in which the transition point between the rectangular cross section of the conductor and the window cross section takes place either steadily (round windows with transition points) or abruptly at a fixed interval from the dielectric (box windows). In this regard, reference is made to "High Power Linear Beam Tubes," A. Staprans et al, in the "Proceedings Of The IEEE", Vol. 61, No. 3, 1973, pp. 299 to 330, particularly Section II D. Window constructions of this type are, indeed, more high-voltage proof, and are more capable of being loaded due to the symmetrical distribution of mechanical and thermal tensions; however, such constructions still exhibit a considerable susceptibility to interference modes. Moreover, the tendency toward oscillation build-up delicately depends upon what degree the symmetry of the arrangement is disturbed, and therefore, for example, to what extent the two rectangular-conductor elements are rotated toward one another. Therefore, radially symmetrical windows require very careful asssembly and, nevertheless, are not completely controllable in their transmission properties and working life properties. These breaks in quality, due to interfering modes, gave rise to a series of counter measures, which are expensive in part; for example, a specific shaping of the dielectric (U.S. Pat. No. 3,594,667).